FR2540485A1 - Sludge thickener comprising settling means and drying means - Google Patents

Abstract

Apparatus for thickening a suspension of solid particles in a liquid, such as a sludge, comprising on the one hand a settling chamber 1 provided with an intake of the suspension to be thickened and settling means 7, and on the other hand means 2 for drying the settled solid particles, characterised in that the drying means 2 comprise a rotating endless screw 9 mounted longitudinally in a cylindrical enclosure 10 which is horizontal or slightly inclined to the horizontal and provided with an exit for dried solid particles situated in the vicinity of the front end of the screw, and in that this cylindrical enclosure 10 is connected with the bottom of the settling chamber 1 by a wide opening extending along the cylinder wall of the enclosure 10 so that the solid particles which have settled fall through this opening into the said cylindrical enclosure 10 and along the endless screw 9, the settling chamber 1 comprising at its upper part an exit for thickening liquid produced during the settling and drying.

Description

 The present invention relates to an apparatus for thickening a suspension of solid particles in a liquid, such as a sludge, comprising on the one hand a settling chamber provided with an inlet for suspension to be thickened and means decantation and on the other hand means for wringing out the settled solid particles.

 Many industries, whether for example the chemical industry, the paper industry or the food industry, are required to reject large quantities of suspension of mineral or organic solid particles in a liquid. In order to recycle this liquid or to reject it without polluting the environment, it is usual to subject these suspensions to clarification by decantation which leads on the one hand to a clarified liquid and on the other hand to decanted solid particles still containing a significant amount of liquid.

 Furthermore, in order to recycle these solid particles and to facilitate handling and / or transport, it is frequent to very significantly reduce their liquid content by wringing.

 It is known to carry out the settling and spinning operations mentioned above, in devices comprising a vertical cylindrical-conical tank fed continuously in suspension, this tank opening at the top of its conical part, in the upstream part of 'A wringing device consisting of a perforated tube forming an enclosure around a rotating endless screw and the downstream end of which is provided with an outlet for drained solid particles. In such devices, the clarified liquid is discharged from the tank by overflowing and the decanted solid particles collect in the conical part, suitable means being provided in the latter for bringing said particles into the wringing device. the screw, by its rotational movement, causes the transfer of the decanted solid particles from the upstream end to the downstream end of the perforated tube, that is to say towards the outlet of solid particles wrung out at the level of which these particles form, possibly in cooperation with appropriate means, a plug which prevents ejection by this outlet, of the wiping liquid and more or less slows down the outlet of the wiped particles which therefore undergo more or less significant compaction. During this transfer, the decanted solid particles are pressed against the thrust face of the threads of the screw, which results in a separation of the liquid and therefore a progressive spinning of the particles, the separated spin liquid being evacuated by the perforations of the perforated tube. The major drawback of these devices lies in the fact that it is frequently necessary to carry out a cleaning of the perforated tube, the perforations of which easily tend to become clogged, clogging which is detrimental to the performance. We have certainly tried to remedy this clogging problem by using a perforated tube having larger perforations; but in this case, a non-negligible quantity of solid particles escapes with the wiping liquid (up to 1 g / l of wiping liquid) through said perforations, which makes it necessary to subject the wiping liquid to further processing.

 The object of the present invention is to remedy these drawbacks by means of an apparatus of the type defined in the first paragraph of this description and which is characterized in that the wiping means comprise a rotary endless screw mounted longitudinally in an enclosure cylindrical horizontal or slightly inclined to the horizontal and provided with an outlet for drained solid particles located in the vicinity of the anterior end of the screw, and in that this cylindrical enclosure communicates with the base of the settling chamber by a wide opening extending along the cylindrical wall of the enclosure, the decantation chamber having at its upper part an outlet for thickening liquid produced during decantation and spinning.

 As this device does not have a perforated tube forming an enclosure around the worm, there is obviously no possible clogging. As for the spin liquid, it is easily evacuated to the settling chamber.

Such an evacuation would only be extremely difficult or even impossible in known devices. Indeed, in the latter, the wringing liquid should be discharged through the very reduced opening ensuring communication between the enclosure containing the worm and the conical part of the tank, this opening being overhung by a large mass and dense of settled solid particles opposing such an evacuation. On the contrary, according to the invention, this opening is not punctual but wide and extending along the cylindrical wall of the enclosure containing the worm. As a result, the decanted solid particles are distributed along the worm which transfers them to the downstream end of the enclosure as they reach the latter thus preventing an accumulation which would be harmful to the evacuation of the wiping liquid. In addition, during this transfer, the thrust face of the threads of the screw exerts pressure on these particles, this pressure having the effect of expressing the liquid retained by said particles; the liquid thus released by the latter is then returned to the settling chamber, progressing easily through a suspension having only a low density of solid particles.

 A particularly effective thickening device is obtained when the cylindrical enclosure and the settling chamber define a single enclosure which is in the form of a bucket with semi-cylindrical bottom in the lower part of which the worm is arranged, the decanting means extending longitudinally in this bucket above this screw. Furthermore, it has been found that when the decantation chamber flares downwards, the voltage phenomena of the decanted solid particles resulting from the attachment of the latter to the walls of said chamber are considerably limited. Such a flared shape therefore has the effect of promoting the flow of the settled particles from the settling chamber towards the cylindrical enclosure.

 It is usual, in particular for suspensions containing very fine solid particles which are difficult to decant, to carry out the prior flocculation of these particles. According to the present invention, this flocculation can be carried out directly in the thickening device which then further comprises flocculation means arranged in the settling chamber or in the bucket above the rear part of the screw without end and upstream of the settling means, the arrival of the suspension to be thickened with added flocculating agents opening out in the vicinity of these flocculation means. Thanks to this arrangement, it is thus possible to reduce, compared with the installations of the prior art, the overall size of the assembly ensuring the flocculation, decantation and wringing operations.

 Advantageously, the decantation means consist of a lamellar separator, preferably co-current.

 According to a preferred variant of the invention, the downstream end of the cylindrical enclosure or of the lower part of the bucket is extended by a cylindrical duct forming an enclosure around an extension of the worm, a particle outlet dewatered solids being provided on this conduit in the vicinity of the anterior end of this extension. The liquid expressed from solid particles subjected to the pressure exerted by the pushing face of the threads of the screw, is evacuated out of this conduit towards the decantation enclosure by sliding on the rear face of said threads.

 It will be noted that the downstream end of the cylinder may advantageously end in a conical part, the top of which carries the exit of dewatered solid particles, the extension of the screw having a conical end coming to be housed in said conical part, this particular shape of the conduit. and of the screw favoring the compaction of the solid particles and, consequently, their spinning.

 It is possible, if desired, to provide means in the vicinity of the outlet for drained solid particles, means for adjusting the degree of spin.

 These means can for example be constituted by a shutter making it possible to adjust the section of the outlet of the drained solid particles. It will be understood that the smaller this section, the more the evacuation of the dewatered particles will be slowed down, the consequence being a more accentuated compaction of these particles and, consequently, a more intense dewatering of the latter.

 In order to allow a symmetrical evacuation of the dewatered solid particles which ensures a uniform dewatering, the axis of the outlet of dewatered solid particles is located in the extension of the axis of the screw and the shutter is arranged symmetrically with respect to the axis of this exit.

 Said means can also consist of the inner wall of the cylindrical duct and / or of the conical part, a wall which has been modified so as to have a high coefficient of friction which slows down the evacuation of the dewatered particles, which results in a further compaction of the latter.

An embodiment of the present invention is illustrated in the description which follows, given with reference to the appended drawings in which
- Figure 1 is a schematic view in longitudinal section of a thickener according to the invention
- Figure 2 is a top view of the thickener of Figure 1;
- Figure 3 is a front view of the thickener of Figure 1; and
- Figure 4 is a front view of the thickener of Figure 1 modified so that its settling chamber flares down.

This thickener comprises a decantation chamber 1 disposed above wiping means 2. The decantation chamber 1 is more precisely delimited by a front wall 3 and a rear wall 4 parallel to one another and by two side walls 5,6 parallel to each other , all these walls being vertical. The chamber 1 also comprises decantation means 7 and an inlet 8 for the material to be thickened consisting of a suspension of solid particles in a liquid such as highly hydrated residual sludge, this inlet 8 opening into this bedroom 1 at the side wall 5
According to the invention, the wiping means 2 comprise an endless screw 9 arranged longitudinally in a horizontal cylindrical enclosure 10, a minimum clearance being left between the top of the threads of the screw and said enclosure 10.

 Furthermore, the latter communicates with the settling chamber through a large opening it formed in the cylindrical wall of the enclosure 10. This opening is more precisely located at the upper part of this cylindrical wall; in addition, it originates at the rear end (or upstream) of the enclosure 10 and extends over the entire length of the latter.

 According to another characteristic of the invention, the side walls 5, 6 of the settling chamber 1 are located in the extension of the cylindrical wall of the enclosure 10, the width of the opening 11 being preferably equal to the diameter of said enclosure 10. The latter and the settling chamber 1 thus define a single enclosure which, as shown in FIG. 3, is in the form of a trough 12 with semi-cylindrical bottom in the lower part of which the screw 9 is arranged , the settling means 7 extending longitudinally in this trough 12 above the screw 9. It will be noted here that according to a particularly advantageous variant as regards the quality of the thickening obtained, the side walls 5,6 and possibly the front 3 and rear 4 walls are arranged so as to define a settling chamber 1 which widens downwards as shown in FIG. 4.

Furthermore, flocculation means 13 are arranged in the decantation chamber 1, upstream of the decantation means 7, the inlet 8 of suspension to be thickened opening out in the vicinity of these means 13. These flocculation means 13 more precisely comprise a series of blades 14 arranged around and along a horizontal shaft 15 disposed above the rear part of the screw 9 and mounted in rotation by means of two bearings
15a, 15b, one of which 15a is carried by the rear wall 4 and the other 15b of which is integral with a support element 15c bearing on the two lateral faces 5,6.

As for the decantation means 7, they consist of a lamellar separator preferably co-current and of known design per se (see in particular the article by Mrs. G. Treyssac and M. Maes published in the review
WATER AND INDUSTRY No. 14, March 1977 - Control of lamellar separation,
Experiments and performances). Schematically, such a separator comprises several groups 16 of plates 17, arranged side by side between the flocculation means 13 and the front wall 3 of the settling chamber 1.

Each group comprises a series of parallel plates 17 arranged one above the other and inclined on the horizontal, their front part being directed downwards, these plates being joined by their ends to the side walls 5,6. It should also be noted that the front wall 3 is slightly lower than the front 4 and side walls 5, 6 so that the settling and dewatering liquid is discharged by overflowing above the wall 3.

 According to the invention, the front (or downstream) end of the cylindrical enclosure 10 is extended by a cylindrical conduit 18 terminated by a conical part 19 whose top carries an outlet 20 preferably cylindrical and horizontal and whose axis is located in the extension of that of screw 9.

 The conduit 18 and this conical part 19 form an enclosure around an extension 21 of the endless screw 9, an extension which has a conical end coming to be housed in said conical part 19, a minimum clearance being left between the tops of the threads of said extension 21 of the screw and on the one hand the conduit 18 and on the other hand the conical part 19. Advantageously, the outlet 20 comprises means 22 for adjusting the degree of wringing of the settled solid particles. These means 22 are constituted by a shutter 23 preferably substantially conical and disposed in the outlet 20 symmetrically with respect to the axis of the latter, the top of this shutter being directed towards the interior of the conical part 19. The base of the shutter 23 is provided with a plate 24 pressed by a spring 25 on the edges of the outlet 20.

 The screw 9 is rotatably mounted via two bearings 9a, 9b, one 9a being carried by the rear wall of the enclosure 10, the other 9b being integral with a support 9e secured to the cylindrical wall of duct 18.

 Drive means 26 for the shaft 15 and the screw 9 are also provided at the rear part of the thickener, these means being able to be constituted for example by a single motor controlling both the shaft 15 and the screw 9 or again by two separate motors, one controlling the shaft 15 and the other the screw 9. Finally, the thickener is completed by feet 27 and possibly by a tank 28 for receiving the thickening liquid, delimited by the wall 3, the upper part of the cylindrical wall of the conduit 18, an extension of the side walls 5,6 and a vertical wall 29 facing the wall 3, this tank 28 being provided with an outlet 30 at its part low.

 The suspension to be thickened enters via the inlet 8 into the thickener which has just been described, and more precisely at the level of the flocculation means 13.

Flocculating agents chosen as a function of the nature of the solid particles to be flocculated will have been added to this suspension beforehand and the resulting suspension / flocculating mixture will be homogenized by subjecting it to vigorous stirring. The suspension thus treated and which enters the thickener is subjected to a light stirring under the effect of the rotational movement of the blades 14, the speed of this movement having to be chosen to promote the formation and the enlargement of the flocs and push them. towards the endless screw 9. It will be noted that as the front wall 3 is less high than the walls 4,5,6, the liquid-floc mixture progresses. from the rear wall 4 to the front wall 3.

 In the flocculation zone, a slight decantation already takes place, and a certain quantity of solid particles in the form of flocs fall on the worm, the phenomenon of decantation continuing and accentuating when the flocculated suspension reaches the decanting means 7 This flocculated suspension crosses one after the other the groups 16 of plates 17. At each group, the suspension circulates between the plates 17, the flocs being deposited on the upper face of said plates. The plates 17 being inclined, the flocs thus deposited slide along this face (this sliding phenomenon being accentuated by the thrust exerted on the flocs by the suspension in circulation) until reaching the front part of the plates 17, zone from which they fall, according to a substantially vertical path between two groups of consecutive plates, in the cylindrical enclosure 10. The suspension is thus gradually rid of its flocculated solid particles . The fluid from the last group of plates is therefore constituted by a suspension with very low density of solid particles which is evacuated from the settling chamber 1 by overflowing above the wall 3.

 It will be noted that since the decantation operation is spread over the entire length of the opening 11 of the cylindrical enclosure 10, the suspension which is located above this opening has a relatively low flock density, this density being, as indicated above, minimum at the outlet of the last group of plates.

 The solid particles decanted in the form of flocs and fallen onto the endless screw 9 are gradually transferred by the latter towards the front end of the cylindrical enclosure 10. During this transfer, these solid particles are pressed against the thrust face threads of the screw 9, this face thus exerting pressure on said particles, this pressure having the effect of expressing the liquid which they contain.

 On the pushing face of each net, a deposit of solid particles is therefore formed, containing less and less liquid as one moves away from the rear wall of the enclosure 10, the liquid expelled particles (wiping liquid) coming to take place between this deposit and the rear face of the following net before rising up along a substantially vertical path towards the settling chamber 1 and being evacuated by overflowing above the wall 3; this ascent is relatively easy since, as indicated above, the suspension circulating in the chamber 1 does not have a density of solid particles sufficiently high to oppose this ascent.

 There is therefore a progressive spinning of the settled particles, from the rear wall to the front end of the enclosure 10. This spinning continues in the cylindrical duct 18 and in the conical part 19, according to a process identical to that described here. above, the spin being however accentuated in said conical part 19 where the solid particles are confined in an increasingly reduced volume. It will be noted here that between the front end of the enclosure 10 and the outlet 20, the solid particles pushed by the threads of the screw and the wiping liquid circulate against the current, respectively towards the outlet 20 along the face thrust of the threads of the extension 21 of the screw 9 and towards the settling chamber 1 by sliding along the rear face of these same threads.

 The dewatered particles arriving at the outlet 20 collide with the shutter 23 closed under the effect of the tension of the spring 25 on the plate 24, shutter which therefore opposes the evacuation of the particles. This results in the progressive formation of a plug of dewatered particles. Due to the existence of this plug, it settles at the downstream end of the conical part 19 a pressure of settlement of the particles increasing due to the progressive contribution of particles, pressure which promotes the desired spinning and evacuation of the liquid separated during this spin. When this pressure becomes greater than the tension of the spring 25, the shutter 23 opens to allow a symmetrical flow of a certain amount of dewatered particles forming the plug and closes as soon as said pressure again becomes less than the tension of the spring. Furthermore, the presence of said plug prevents the evacuation of the wiping liquid through the opening 20; therefore, as it separates from the particles, this wiping liquid flows towards the settling chamber 1. It should be noted, however, that the packing effect mentioned above can be obtained, although to a lesser degree, in the absence of the shutter 23 and of the spring 25. In fact, there is also in this case formation of a plug of wiped particles between the last anterior thread of the extension 21 of the screw 9 and the opening 20, this plug slowing down the flow of the particles wrung out by the said outlet 20 and thereby ensuring the desired settlement. In this case, it is also possible to accentuate the settlement somewhat, using a tube 18 and a conical part 19, the inner wall of which has been modified so as to have a high coefficient of friction which slows down the exit of the dewatered particles. This modification of the inner wall may consist either in the deposition on this wall of a coating with a high coefficient of friction and constituted for example, by a layer of neoprene paint or by a thin layer of rubber, or in the physical treatment of this wall to modify the surface condition, such treatment could for example consist of sanding.

 It is of course possible to make various modifications to the device which has just been described without, however, departing from the scope of the invention.

 Thus, for example, it would be possible to use other types of settling means, these nevertheless having to be designed so as to extend above and along the opening 11 and mention will be made, for example, of the separators lamellar with cross currents also described in the article mentioned above which appeared in the review L'EAU ET. INDUSTRY. Likewise, it would be possible to use an endless screw 9 and an extension 21 having the improvements described in French patent No. 8301646.

Claims (12)

 1. Apparatus for thickening a suspension of solid particles in a liquid, such as a mud, comprising on the one hand a settling chamber (1) provided with an inlet (8) of suspension to be thickened and decanting means (7) and on the other hand means for wiping (2) the decanted solid particles, characterized in that the wiping means (2) comprise a rotary endless screw (9) mounted longitudinally in an enclosure cylindrical (10) horizontal or slightly inclined to the horizontal and provided with an outlet for drained solid particles located near the anterior end of the screw, and in that this cylindrical speaker (10) communicates with the base of the decantation chamber (1) by a wide opening (11) extending along the cylindrical wall of the enclosure (10), so that the decanted solid particles fall through this opening (11) in said cylindrical enclosure (10) and along the worm (9), the chamber decantation (1) having at its upper part an outlet for thickening liquid produced during decantation and spinning  2. Apparatus according to claim 1, characterized in that the cylindrical enclosure (10) and the settling chamber (1) define a single enclosure which is in the form of a trough (12) with a semi-cylindrical bottom in the part lower of which is disposed the worm (9), the settling means (7) extending longitudinally in this bucket above this screw.  3. Apparatus according to claim 1 or 2, characterized in that the settling chamber (1) widens downwards.  4. Apparatus according to claim 1, 2 or 3, characterized in that it further comprises flocculation means (13) arranged in the settling chamber (1) or in the bucket (12) above the posterior part of the worm (9) and upstream of the settling means (7), the inlet (8) of the suspension to be thickened with added flocculating agents opening out in the vicinity of these flocculation means.  5. Apparatus according to any one of the preceding claims, characterized in that the decanting means consist of a lamellar separator (16, 17).  6. Apparatus according to claim 5, characterized in that the lamellar separator is co-current.  7. Apparatus according to any one of the preceding claims, characterized in that the downstream end of the cylindrical enclosure (10) or of the lower part of the bucket (12) is extended by a cylindrical conduit (18) forming enclosure around an extension (21) of the worm (9), an outlet (20) of dewatered solid particles being provided on this conduit in the vicinity of the anterior end of this extension.  8. Apparatus according to claim 7, characterized in that the downstream end of the cylindrical conduit (18) ends in a conical part (19) the top of which carries the outlet (20) of dewatered solid particles, the extension ( 21) of the screw (9) having a conical termination which is received in said conical part (19).  9. Apparatus according to any one of the preceding claims, characterized in that in the vicinity of the outlet (20) of dewatered solid particles, means (22) for adjusting the degree of wringing.  10. Apparatus according to claim 9 comprising the cylindrical conduit (18) receiving the extension (21) of the worm, characterized in that these adjustment means (22) are constituted by a shutter (23, 24) for adjust the section of the outlet (20) of dewatered solid particles.  11. Apparatus according to claim 10, characterized in that the axis of the outlet (20) of dewatered solid particles is located in the extension of the axis of the screw (9) and in that the shutter is arranged symmetrically relative to the axis of this outlet (20) so as to have a symmetrical evacuation of the dewatered solid particles.  12. Apparatus according to claim 9 comprising the cylindrical conduit (18) optionally terminated by a conical part (19) and receiving the extension (21) of the worm (9), characterized in that the adjustment means (22 ) consist of the inner wall of the cylindrical duct (18) and / or of the conical part (19), a wall which has been modified so as to have a high coefficient of friction.